Film grain is formed during the creation of motion picture images. Film grain is most noticeable in high definition (HD) images and becomes a distinctive cinema trait that must be preserved through the whole image processing and delivery chain. Nevertheless, film grain preservation is a challenge for current encoders, because compression grains related to temporal prediction cannot be exploited. Because of the random nature of the film grain, visually lossless encoding is only achieved at very high bit rates. Lossy encoders tend to suppress the film grain when filtering the high frequencies typically associated with noise and fine texture.
Some film grain technologies explore an implementation that involves lookups from a large database. This approach may be very difficult for modern cost-sensitive DVD players. If film grain is added during decoding, the decoder has to write reference pictures to memory twice. In this regard, writing occurs once with grain, and again without grain to facilitate in-loop processing. Adding film grain during decoding also presents problems for video processes such as de-interlacing, MPEG artifact reduction such as de-blocking and de-ringing, and video enhancements such as sharpening and histogram equalization.
If film grain is added during display, some existing technologies recommend computation of an 8×8 average, which becomes problematic. For example, assign film grain during display will require reading each picture twice, buffering 7 lines of video, or passing parameters between decode and display. These tasks may be very difficult to coordinate properly. Adding film grain during display also creates problems for interlaced displays and if done improperly, temporal statistics of the film grain will be incorrect.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.